Mail processing systems, such as, for example, a mailing machine, often include different modules that automate the processes of producing mail pieces. The typical mailing machine includes a variety of different modules or sub-systems, each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. Such modules could include, for example, a singulating module for separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a stripping/moistening module for stripping open the flap of an envelope and wetting and sealing the glued flap of an envelope, a weighing module for weighing the mail piece, and a metering/printing module for storing postage amounts and applying evidence of postage either directly to the mail piece or to a tape to be applied to the mail piece. The mailing machine is controlled by a central processing unit that executes software stored in memory provided in the mailing machine. The exact configuration of the mailing machine is, of course, particular to the needs of the user.
The metering/printing modules of many current mailing machines utilize ink jet printing technology to print evidence of postage, such as postal indicia that include a 2-D barcode. Ink jet printers are well known in the art. Generally, an ink jet printer includes one or more arrays of nozzles (sometimes referred to as orifices), a supply of ink, a plurality of ejection elements (for example, heater elements or piezoelectric transducer elements) corresponding to the nozzles and suitable driver and control electronics for controlling the ejection elements. Typically, the one or more arrays of nozzles and the ejection elements along with their associated components are referred to as a print head. It is the activation of the ejection elements that causes drops of ink to be expelled from the nozzles. The ink ejected in this manner forms drops which travel along a flight path until they reach a print medium such as a sheet of paper, an envelope or the like. Once they reach the print medium, the drops dry and collectively form a print image. Typically, the ejection elements are selectively activated (energized) or not activated (not energized) to expel or not expel, respectively, drops of ink as relative movement is provided between the print head and the print medium so that a predetermined or desired print image is achieved.
The transport mechanism of a mailing machine also typically includes an encoder system that acts as a mechanical timer for generating firing pulses for the print head and thus synchronizing the printing operation with the motion of the mail pieces. One example of an encoder system includes an encoder disk that has a plurality of apertures located around its circumference, a light source and a light detector. As the transport mechanism conveys mail pieces along the mailing machine, it causes the encoder disk to rotate. The encoder disk, the light source and the encoder detector are positioned with respect to one another so that the encoder disk causes the light source to be alternately blocked and unblocked as the encoder disk rotates. The transition from blocked to unblocked or vice versa provides a synchronization signal for timing of print head firing pulses. Thus, as will be appreciated, the timing of the printing by the print head is tied to the movement of the mail pieces.
As noted above, images such as postal indicia are printed by metering/printing modules of mailing machines to evidence that accounting has occurred for the appropriate postage for the mail piece. A typical postal indicium includes fixed elements such as city name, state, a graphic, meter serial number, etc., and variable information such as date, postage amount, an encrypted number, etc. Postal indicia have been printed by flat bed printers, rotary printers and ink jet printers. The improvement of photocopying, printing and scanning equipment over time has made it easier to commit fraud by copying and reusing postal indicia.
The possibility of fraud also exists in many other printing applications. For example, ticketing companies are currently giving purchasers the option of printing their electronic tickets at home, using ordinary paper, a personal computer printer, and an Internet connection. One of the problems in allowing people to print tickets at home is how to ensure that the tickets are not counterfeited. One of the solutions suggested to solve the foregoing problem is to print an encrypted bar code on the ticket. Unfortunately, a ticket printed on ordinary paper with an encrypted bar code can be photocopied, thereby making it difficult to distinguish between the original, genuine ticket and a photocopied ticket.
One method currently used to deter copying of images such as postal indicia is to use specialty inks, such as specialty tagged fluorescent inks. However, a counterfeiter could obtain a specialty ink and use it with an off-the-shelf printer. Further, as many printing applications that require security are moving to the use of conventional black ink, this method obviously would not be available to prevent fraud. Thus, there is a need for a method for deterring copying and preventing fraud that is independent of the use of a specialty ink.